If you're feeling creeped, threatened, or scared then stay in groups with your friends. Notifying con staff/proper authorities will help and while you may not want to for fear that you're hassling them, remember that they're there for a reason. I can assure you, they won't turn you down or act like you're being a nuisance. Or if you feel like you don't want to jump right to telling the staff over something that could be seem as trivial or easily handled without their help, at least keep a staffer in sight so you have the option.

As for you yourself handling it... you might just have to be assertive and let him know how he's coming off to the two of you and that you want it stopped.